Gob-Side Entry Retaining Technology with Advanced Empty Hole Butterfly-Shaped Weakening in Three-Soft Coal Seam in China

Table 1

Physical and mechanical parameters of rock mass.

Lithology	Bulk weight (kN/m^3)	Compressive strength (MPa)	Tensile strength (MPa)	Elastic modulus (MPa)	Cohesion (MPa)	Internal friction angle (°)	Poisson’s ratio
Siltstone	26.7	39.3	3.12	3.0 × 10^4	6.5	33	0.22
Argillaceous siltstone	26.6	34.8	3.72	3.1 × 10^4	5.7	38	0.16
No. 3 coal seam	13.8	7.9	0.39	0.5 × 10^4	1. 7	31	0.24
Siltstone	26.1	21.0	1.15	1.4 × 10^4	3.5	35	0.20
Next slice of no. 3 coal seam	13.6	7.5	0.31	0.5 × 10^4	1.6	31	0.23
Siltstone	24.9	30.3	2.65	3.4 × 10^4	3.6	30	0.22